Convert square inches to square feet (sq in to sq ft)

One square inch is exactly 1/144 of a square foot, because a foot is 12 inches and area squares the factor: 12 times 12 is 144. That follows from the definition of the foot and needs nothing else.

Worked through: 288 sq in x 0.0069444444 = 2 sq ft.

Going the other way, one square foot is 144 square inches.

For mental arithmetic: Divide by 144: divide by 12 twice. Or convert both sides to feet before multiplying.

The mistake to watch for is dividing by 12. A sheet measured as 24 by 36 inches is 864 square inches, and 864 divided by 12 is 72, which sounds like square feet and is wrong by a factor of twelve. The right answer is 6. Where it comes up is anything priced per square foot and measured with a tape in inches: glass, countertop stone, sheet metal, tile, signage and printed graphics. The safer method is to convert each side to feet first and then multiply: 2 feet by 3 feet is 6 square feet, and the arithmetic cannot square the wrong number.

Precision is worth matching to the input. A measurement given as 12 sq in carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.